DraStic is a popular DS emulator for Android devices.
Originally it was a paid app, but when Yuzu was taken down after Nintendo issued a lawsuit against Tropic Haze accusing the company's product for supposedly piracy, Exophase announced his product, DraStic, for free. However he also declared that sometime after, it will be delisted from Play Store and will also make his product open-source.
The zip file has the split APK, and the Split APK Installer.
Here's how to install it:
1. Use a file manager (example: ZArchiver Pro)
2. Extract the zip file into a folder, for example:
/storage/emulated/0/DraStic
3. Install the Split APK Installer provided.
4. Open the installed app.
5. Click the button "Internal file picker", DO NOT click the one under it "System file picker", this will request the Android system to find any files that are APKs or XAPKs.
Note for step 5: If it asks for access to the file system, allow it.
6. Look for the folder you extracted the zip file you downloaded. When you do, look for the folder within the extracted folder, which is: DraStic_com.dsemu.drastic
7. Select base.apk, then split_config.armeabi-v7.apk, then split_config.xhdpi.apk, and lastly split_config.en.apk
8. Click "Install" when you scroll down.
9. A prompt (or a window for older Android systems) will appear, click on "Install".
Note for step 9: Since you're installing from a third-party source, it will block you stating that it doesn't allow unknown sources, but you can allow it in Settings.
10. The icon (which may look like the head of Droid in front of a blue grid) should change to a circle with a picture of a DS.
11. If successful, then you'll see the menu.
12. You're ready for DS gaming. Prepare some roms of your favorite games and play it in DraStic. You may be asked for access to files when you go to select a folder that you put your roms inside.
NOTE: I will not provide ROM sites for DS for the safety of my post, and because of Nintendo.